000
FXUS63 KIND 200800
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
300 AM EST Tue Feb 20 2018
.UPDATE...
The LONG TERM and AVIATION Sections have been updated below.
&&
.SYNOPSIS...
Issued at 408 PM EST Mon Feb 19 2018
A frontal system will meander across the area into the weekend,
keeping rain around for much of the period. The rain may be heavy at
times. Temperatures will remain above normal through the period,
with record temperatures possible on Tuesday.
&&
.NEAR TERM.../Rest of This Afternoon and Tonight/
Issued at 408 PM EST Mon Feb 19 2018
Strong low level flow continues to bring plentiful moisture into
central Indiana this afternoon. Rain was mainly confined to the
northwest half of the forecast area, which is being influenced by
upper impulses riding around an upper ridge.
This trend will continue through the night as strong southerly flow
remains in place across the area. The upper ridge will keep part of
the southeast forecast area dry, while the northwest forecast area
continues to be impacted by waves moving through the flow.
Plentiful moisture will be in place thanks to the strong low level
flow. Will go high PoPs tonight across the northwest, with chance in
the middle, and dry to slight chance PoPs southeast.
Parts of the northwest forecast area have already received over an
inch of rain today. Precipitable water values are over 300 percent of
normal. Models show axis of heaviest rain just northwest of the
forecast area tonight, but a small shift could bring it into the
area. Given the above have decided to issue a small Flood Watch for
the extreme northwest forecast area, starting tonight and continuing
into Wednesday.
Temperatures will not fall a whole lot tonight with the good
southerly flow. Thus went with lows only around 60 most locations,
which would set a new record high minimum temperature for
Indianapolis.
&&
.SHORT TERM.../Tuesday through Thursday/
Issued at 408 PM EST Mon Feb 19 2018
Models are close enough that the model blend initialization
was accepted for most items.
The upper high to the southeast and a low level jet will continue to
bring in unseasonably moist air into the area into Wednesday. The
upper high will nose into the forecast area enough that focus for
rain will be on the northwest half of the forecast area until
overnight Tuesday night. At that time, a cold front will move into
the area and bring more widespread rain Wednesday.
Will keep likely or higher category PoPs contained to the northwest
half or so of the area through 06Z Wednesday, then allow high PoPs
most areas through 18Z Wednesday. As the front shifts to the south,
a wave will ride along it and keep rain chances into Thursday
morning. There is some model differences in this wave, with the NAM
being farthest north.
Will stick with the blend for now and keep some high PoPs across the
southeast half of the forecast area into Thursday morning. If the
wave ends up farther south, then PoPs may be lowered some Wednesday
night into Thursday.
Threat for heavy rain continues with the plentiful moisture. For now
will keep the Flood Watch confined to the far northwest, but it may
be expanded for Tuesday night into Wednesday as the front moves into
the area.
Looking beyond the rain, winds will be a factor on Tuesday. Strong
winds aloft may mix down some, especially for areas that see a break
in the clouds. Momentum transfer forecasts from the models show near
35kt possible, so will include a mention of 40mph gusts on Tuesday.
It appears that record temperatures will be seen on Tuesday, with
highs in the 70s, perhaps to near 80 in the far south. How high
things go will depend on cloud cover.
As colder air moves in behind the front on Wednesday night and
Thursday morning, there could be some light mixed precipitation
across the north. Although air temperatures may be cold enough for
freezing rain, the ground should still be warm enough from the
record temperatures to minimize any impact.
&&
.LONG TERM /Friday through Monday/...
Issued at 300 AM EST Tue Feb 20 2018
The wet and active pattern will continue through much of the
weekend with the weather finally settling down late Sunday into
Monday as the amplified upper flow regime finally relaxes and high
pressure builds into the region.
Solid model consensus for Friday and Saturday with the frontal
boundary lifting back north across the region as multiple surface
waves track along it. This will provide a renewed threat for
rain...heavy at times...and flooding when adding the expected
rainfall over the next few days prior to the extended period.
After some drying on Thursday with the front off to the
south...the initial wave of moisture will arrive early Friday and
linger through the day. A brief respite Friday evening will be
followed by a secondary wave late Friday night into Saturday as
the frontal boundary lifts into the northern half of the forecast
area. This will bring an additional round of rain with embedded
thunder as elevated instability lifts into the region.
The final surface wave is poised to swing through the area
Saturday night into Sunday morning. The op GFS deviates from the
consensus at this point by sending up a rapidly intensifying
surface low into the Great Lakes. Most of the model data including
the bulk of the ensemble members favor a less wrapped up wave
that tracks along the boundary across the region Saturday night.
Even with this solution...the final surface wave will bring a
third round of moderate to heavy rain with a convective component
along and ahead of the cold front.
Potential for an additional 2 to 4 inches of rain with locally
higher amounts from Friday through early Sunday with precip water
values once again rising to climatological maxes for late
February. Taking into account expected rainfall through
Thursday this will only exacerbate flooding concerns into the
weekend...especially for rivers and streams...and in lowland and
poor drainage areas.
Once the front shifts east during the day Sunday...drier weather
will finally arrive as high pressure builds into the Ohio Valley
and the amplified upper level pattern across the country this week
relaxes back to more of a quasizonal regime. Highs Friday and
Saturday have the potential to rise into the 60s once again south
of wherever the front eventually lays out. Behind the system
Sunday and Monday...temperatures will remain mild with highs
ranging from the upper 40s into the 50s.
&&
.AVIATION /Discussion for the 200900Z TAF Update/...
Issued at 300 AM EST Tue Feb 20 2018
Pulling back on any precip mention at all terminals except KLAF
for the rest of the overnight. Still appears the next surge of
moisture will bring increased rainfall coverage to the northwest
half of central Indiana by mid morning...potentially impacting
KHUF and KIND.
06Z discussion follows.
VFR much of the period. MVFR will be possible at HUF and
especially LAF.
Rain showers will be present at or near LAF much of the period,
and may overspread the other sites later in the period.
Winds and wind shear will be of impact during this period, with
gusts at times ranging from 23-34KT, generally from 190-210.
Sustained winds will be 9-18KT.
Low level winds around 2kft will be as strong as 45-55KT, and will
carry wind shear at all sites.
Visibilities will occasionally be impacted by rain and fog, and
will be MVFR at times, particularly at LAF.
&&
.HYDROLOGY...
Issued at 408 PM EST Mon Feb 19 2018
Potential for significant flooding continues across the area this
week.
Precipitable water values will be near the climatological maximum
into mid-week as the strong low level jet continues to pump in
moisture from the Gulf of Mexico. This will be briefly pushed south,
but then the values will return late week.
Parts of the northwest forecast area have already received over an
inch of rain into early Monday afternoon. Perceptible water values
were over 300 percent of normal. Thus a Flood Watch was issued for
the extreme northwest forecast area, since the heaviest rain may
fall in this area tonight into Tuesday night.
Elsewhere it looks like the threat for heavier rain with the first
system will come Tuesday night into Wednesday. A Flood Watch may
have to be issued for that period if trends continue.
The threat for heavy rain and flooding will return late week as
moisture returns into the area.
Some rivers are forecast to go into moderate flooding based on the
expected rainfall. See river forecasts for more details.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Wednesday morning for INZ021-028-029.
&&
$$
SYNOPSIS...50
NEAR TERM...50
SHORT TERM...50
LONG TERM....Ryan
AVIATION...Nield/Ryan
HYDROLOGY...50/Ryan